1. Field of the Invention
This invention relates to a sprayable liquid biocontrol formulation comprising dispersed starch-based bioplastic imbedded with microbial biocontrol agents which is delivered to targets, such as pathogens and foliage, to decrease contamination and infestation of agricultural products. The present invention provides examples of spraying the biocontrol formulation comprising an entomopathogenic isolate of Beauveria bassiana or an endotoxin produced by Bacillus thuringiensis to effectively control infestation in corn by the European Corn Borer, delivering the sprayable biocontrol formulation comprising a non-toxigenic Aspergillus flavus strain to crops to effectively reduce aflatoxin contamination in corn and other crop plants, and to applying the sprayable biocontrol formulation comprising Trichoderma harzianum to tomato seeds to effectively reduce damping off. Additionally, this sprayable bioplastic formulation is also used for carrying spores of a Beauveria bassiana strain for controlling the Tarnished Plant Bug in cotton.
2. Description of the Relevant Art
The general term microbial biocontrol agents refers to the use of microorganisms in the control of agricultural pests, including bacteria, fungi, weeds and insects. Although the literature reports many examples of effective microbial isolates for controlling specific pests or plant pathogens under laboratory or small-scale field conditions, only a limited number have entered into the marketplace. A large number of factors may influence the performance of microbial biocontrol agents given that they are living organisms, different from synthetic agrochemicals. In several cases, lack of consistent field efficacy, high production costs, and product variability have limited their commercial success (Glare et al. 2012. Trends in Biotech. 30:250-258). However, the most important factor limiting the practical use of microbial biocontrol agents in agriculture is related to how these biocontrol microorganisms are formulated (Legget et al. 2011. Can. J. Plant Pathol. 33:101-107). Other than serving for delivering microbial biocontrol agents to the target (i.e. soil or foliage), formulation should also guarantee adequate shelf life, easy handling and safety to operators, and prolonged bioactivity of biocontrol microorganisms after field application (Fravel, D. R. 2009. Annu. Rev. Phytopathol. 43:337-359; Legget et al., supra). Inadequate or inappropriate formulation is consequently the most common reason limiting the use and diffusion of microbial biocontrol agents in agriculture (Kaewchai et al. 2009. Fungal Diversity 38:25-50). Recently, advancement in biotechnology and applied biology, and the increasing demand for safety of food products and environmental sustainability, have resulted in an increased demand for effective microbial biocontrol agents and consequently the development of new technical approaches (Leggett et al., supra; Glare et al., supra).
As mentioned above, microbial biocontrol agents are mainly represented by bacteria or fungi which are used for controlling pests, plant pathogens and weeds in agriculture. In addition to the bacterium Bacillus thuringiensis, other successful examples of biocontrol agents are the fungi Trichoderma spp. and Beauveria bassiana (Kaewchai et al., supra; Glare et al., supra). These two filamentous fungi are formulated in a variety of different delivery systems, comprising pre-gelatinized starch-flour, granules of semolina flour and clay, inoculated grains, wettable powder, etc. (Papavizas 1985. Annu. Rev. Phytopathol. 23:23-54; Daigle and Cotty 1997. Biocontrol Sci. Technol. 7:3-10; Harman et al. 2011. Phytoparasitica. 39:103-108).
Many other biocontrol fungi, including atoxigenic isolates of the fungus A. flavus, which are currently being used for reducing aflatoxin contamination in corn, cotton and peanuts, are formulated following similar techniques and approaches, (Dorner, J. W. 2004. Toxin Rev. 23:425-450; Abbas et al. 2006. Biocontrol Sci. Technol. 16:437-449). Aflatoxins refer to a group of carcinogenic mycotoxins mainly produced by the soil-inhabiting fungus A. flavus. An innovative and successful approach for reducing aflatoxin contamination in corn is a biocontrol strategy consisting of the use of atoxigenic isolates of A. flavus to competitively exclude indigenous aflatoxigenic isolates. Studies conducted in Southern USA have demonstrated that soil application of cereal grains inoculated with atoxigenic isolates of A. flavus were successful in reducing aflatoxin contamination in corn, cotton and peanuts (Dorner, J. W, supra; Abbas et al., supra). In addition, a biocontrol formulation consisting of spore-coated barley seeds has been commercialized in the USA. More recent studies have shown that cereal grains can be efficiently replaced by granules made of the starch-based bioplastic Mater-Bi™ (MB) (Accinelli et al. 2009. Bioresource Technol. 100: 3997-4004; Accinelli et al. 2012. Crop Protection 32:30-35; Abbas et al. 2012. U.S. Pat. No. 8,173,179). Similar to A. flavus, a variety of other filamentous fungi are capable of growing on starch-rich substrates (Accinelli and Abbas. 2011. Toxin Rev. 30:71-78). Consequently, the concept of using a starch-based bioplastic matrix to deliver fungal propagules has been extended to the biocontrol fungus Trichoderma spp. (Abbas et al. 2012. US Published Application No. 20120213740; Accinelli et al. 2014. Acta Hort. 1015:79-88).
The original concept consisted of a granular starch-based bioplastic formulated to serve as a carrier matrix to sustain growth of soil-born biocontrol fungi and to provide a mechanism for inoculation of corn field soil. The bioplastic granules are composed of starch-based polymers stabilized by chemical cross linking. Bioplastic granules promote intense fungal growth and sporulation which results in rapid soil colonization. In addition, bioplastic granules are produced from renewable and compostable sources.
Various biocontrol methods and formulations for effective control of toxigenic fungi and bacteria and insect pests are known in the art, as discussed above. However, there still remains a need for formulations of biocontrol agents which are effective for ensuring the integrity and effectiveness of the biocontrol agent after long term storage, and for facilitating handling, safety, timing and positioning of application of the biocontrol agent in the field and in the greenhouse. The need for suitable, effective formulation systems to deliver other biological control agents is also evident.